JPS61250188A - Method of hydrodimerization of acrylonitrile - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION TECHNICAL FIELD The present invention relates to an electrolytic process for the synthesis of organic compounds, and in particular to a method for producing adiponitrile.

BACKGROUND OF THE INVENTION Adiponitrile is used extensively in the production of synthetic fibers of the nylon 66 type and in several other organic synthesis processes.

One of the simplest known methods for producing adiponitrile involves hydrodimerization of acrylonitrile. In the electrolysis process, adiponitrile is used as the cathode (c
Oxygen is generated at the anode and oxygen is generated at the anode.
e). Empirically, this is represented by the following formula: (Cathode reaction) 2CII 2CIICN + 21120 + 2e-
"NC(CH2) 4CN + 2011-(anodic reaction) 20H--402+lI20 +2e'"The thermodynamic-electrochemical total conversion efficiency is never achieved in practical electrolytic cells such as those mentioned above, therefore, different polarizations, e.g. In order to overcome the ohmic resistance of the electrolytic cell and the back emf generated by the consumption of reactants and the formation of products and the activation polarization due to the irreversibility of the electrode reactions, a voltage higher than the theoretical voltage is applied to the electrolytic cell. must be given.

Typically, anodic reactions, ie, oxygen evolution, are carried out using carbon steel anodes and are characterized by high polarization, which can be O, aV or higher. These polarizations result in significant electrolytic power consumption (IE).

Therefore, as a process for electrohydro-dimerization of acrylonitrile to produce adiponitrile,
Processes that can reduce electrolytic sliding power consumption are continually being sought.

DISCLOSURE OF THE INVENTION The present invention is directed to a low energy process for the hydrodimerization of acrylonitrile to produce adiponitrile in an electrolytic cell. The electrolytic cell includes an anode, a cathode, and a water-soluble electrolyte. An electrolyte solution is maintained in contact with the cathode and anode. A source of acrylonitrile is kept at the cathode and a source of hydroxide ions is kept at the anode. A direct current is passed through the system to cause the hydrodimerization of acrylonitrile to adiponitrile at the cathode and the anode. The anode of the present invention consists of a layer of NiCo2O4, optionally containing a fluorinated hydrocarbon polymer, adhered to an electrically conductive substrate. In this process, the electrode area l cm
At a current density of 100 mA per 2, the required anode voltage is less than about 2000 mV.

The present invention represents a significant advance in electrochemical engineering, particularly in the adiponitrile industry. Electrochemical processes that utilize anodes containing NI Co 204 catalysts for the hydrodimerization of acrylonitrile to adiponitrile require low anode voltages, allowing for significant energy savings.

Other features and advantages of the invention will become apparent from the following description, from the claims, and from the drawings showing exemplary embodiments of the invention.

DETAILED DESCRIPTION OF THE INVENTION In general, conductive electrode materials compatible with acrylonitrile electrohydrodimerization systems and oxygen-evolving environments may be used to fabricate the anode substrate. It is particularly preferred that the substrate is a metal substrate such as nickel, stainless steel, carbon steel, copper, lead, cadmium, zinc. It is particularly preferred that a carbon steel substrate be used; optionally, the substrate can be waterproofed with about 2 to about IQmg per 1.5 m of polytetrafluoroethylene (PTFE polymer from DuPont) or fluorinated ethylene propylene. Typically the substrate is in the form of a sheet with a plurality of holes, preferably a screen material, but also a sheet of flat metal.A typical substrate has a diameter of about 5 ml (12,7 μm) to about 20m1 l (5
Typical mesh sizes range from a low of about 50 meshes to a high of about 200 meshes, preferably about 100 meshes.

Mesh refers to the number of wires per linear inch in each axis.The metal substrate may be manufactured by conventional methods and may be manufactured using 10200 carbon fibers from Cleveland Wire and Manufacturing Co., Cleveland, Ohio. May be purchased as m#100 mesh screen.

The conductive electrode substrate typically supports a N i Co 204-binder layer, referred to as the catalyst layer, although generally any binder compatible with the acrylonitrile electrohydrodimerization system may be used; Fluorinated hydrocarbon polymers with a molecular weight greater than 101 are preferred, it is particularly preferred that the binder is PTFE,
Generally the mixture is about 20 wt% to about 80% binder.
, preferably 25%, and also about 8% for about 20% catalyst.
0%, preferably 75%. Typically the catalyst layer is about 1
mil (25,4 μm) to approximately 5 ml (12
7 μm), preferably about 2.5 mil (60,4
The average diameter is about 0.1 μm to about 8 μm, preferably about 0.5 μm.

The substrate and catalyst layer form a conventional gas diffusion electrode and can be fabricated by methods known to those skilled in the art. However, NiCo2O4 powder can be made into steel by several other methods. Pyrolysis of mixed nitrides of nickel and cobalt is the most common method. Thus, the above anode can be manufactured by first intimately mixing appropriate amounts of an aqueous dispersion of NiCo20◆ powder and an aqueous dispersion of PTFE. The mixed solids, depending on the consistency of the co-dispersion, can then be deposited onto the substrate by a spraying, filtration or printing process.

It is particularly advantageous to add flocculants to the codispersion which flocculate the suspended solids. The resulting eutectoid is filtered onto a filter paper and the filter coke is conveyed under pressure to a screen substrate.

After drying and densification of the catalyst layer, the electrodes are cured (e.g. sintered) to bond the structures together by curing the PTFE polymer and finally heated to 320°C and 35°C for 10 minutes in air.
Heated at a temperature between 0°C.

The anode described above is utilized in combination with a conventional cathode used for the electrohydrodimerization of acrylonitrile to adiponitrile. These cathodes include bridges made from lead, cadmium, zinc, graphite, carbon steel, titanium, nickel, and copper.

The electrolyte system is conventional, typically 7 and 10
containing an electrolyte such as a Na2HPO4-based system with a pH between . It is common practice to use a different electrolyte composition in the anode compartment than that used in the cathode compartment. Typically, additives such as corrosion inhibitors may be added to the electrolyte system. Additionally, typical electrolytic cells operate at 54°C.

Monsanto Co.
rp.

Any commercially available good grade acrylonitrile is suitable for electrohydrodimerization, including acrylonitrile available from Ration.

The conventional electrolyzer and electrohydro-dimerization process was described by Danly, D.E.
Adiponitrile (Adi) via improved EHD
Ponitrile via Improved EH
D) J, Hydrocarbon Processing (llydroc
arbon Processing), April 1981, the contents of which are incorporated herein by reference. In this process, an electrolyte solution is kept in contact with both electrodes to close the electrical circuit. In adapting this process as disclosed herein, hydroxide ions are supplied to the anode using techniques conventional in the fuel cell art, eg, from the cathode chamber by diffusion through the electrolyte. Acrylonitrile is supplied to the cathode by conventional means, such as by circulating a fluid vapor containing acrylonitrile, water and dissolved salts to the cathode chamber of the reactor. Preferably, fuel gas and acrylonitrile are continuously supplied to each electrode as the electrolysis products are removed (a continuous process as opposed to a batch process), about 20 mA/cs.
Electrolysis occurs when a current with a current density of from 250 mA/am2 to about 250 mA/am2 is applied to the electrode. At the cathode, acrylonitrile is hydrodimerized to adiponitrile.
Empirically, this is 2CII 2CHCN + 211
zO+ 2e--=NC(C112)4CN+2011
In the anode of the present invention, hydroxide ions are oxidized to produce oxygen, which for hydrogen is expressed empirically as H2+20H''→21120+2e'''. Typical yield of adiponitrile is about 60%
and about 90%.

EXAMPLE A Pyroceram (Corning Glass Works Company) dish was placed in an open placed in a vented fame hood and heated to 350°C.

29 g of Ni (Not)2.6H20 and 58 g of Co (NO3)2.6H20 were added to the beaker;
It was melted at 135° C. for about 30 minutes. The molten solution was quickly poured onto Pyroceram at 350°C and heated in air at 350°C for an additional 2.5 hours.

Cooling was then allowed and the product was passed through a 100 mesh screen and heated at 350°C for an additional 2 hours.
heat treated. This process produced a fine black powder of Ni Co 204 composition.

3g NiCo2O4 8Q at 200W for 2 minutes
Ultrasonically blended with ml water. 1.0 g (dry solids basis) of PTFE T-30 polymer (DuPont) solution was added and blending was continued for 1 minute. The blended solids were filtered into 12.5cm x 12.
It was fed onto a 100 mesh screen of 5 gm carbon steel. Drying at 120°C and 400 ps i (
After compression at 28 kg/coI'), the electrode was sintered at 321° C. for 10 minutes in air. This electrode is 1
0% Na2HPO4, 3, 8% Na2B+Ov・1
Tested in an aqueous solution containing OH20 and 0.4% ethyldibutyl ammonium phosphate. Testing of an electrode in a typical electrolyte solution used in an electrohydrodimerization process utilizes the anode, since that anode is independent of the rest of the electrolytic cell. is sufficient to demonstrate the effectiveness of

The results of the test are shown as curve 2 in the drawing.

In the drawing, the X axis represents the current density of the electrolytic cell as mA/elI2 of the electrode.
It is expressed as This is the anode voltage (y) in mV
is plotted against. The anode voltage is not an absolute value, but a relative value to the hydrogen/platinum electrode in the same solution used as the reference electrode (HRE). The HRE voltage is assumed to be zero 1, indicated by the 0 point.
23 V is the theoretical voltage required to generate oxygen from the anode 0 curve l is N a 2 HP O
The actual amount required to generate oxygen from a carbon steel electrode in a solution of The voltage, @element generation data curve l, was taken from the Danley paper. The difference between the curve and 1.23 V is the polarization defined as the differential voltage at which the observed decomposition voltage of the aqueous electrolyte exceeds the theoretical reversible decomposition voltage. In contrast to curve 1, curve 2
shows the voltage required for an anode containing NlCo2O4 in a similar electrolyte solution. For example, at a current density of 100 mA/as'' in the electrode area, approximately 2000 m
There are voltage requirements lower than V. As is clear from the comparison between curve 2 and curve 1 at a specific current density, N
The voltage required by an anode containing iCo 204 is lower.

These electrolyzers make a significant contribution to electrochemical engineering, particularly to the adiponitrile industry, by employing energy-saving anodes containing N I Co 2 Q 4 . The power consumption for electrohydrodimerization of acrylonitrile to adiponitrile is related to the voltage required for the anodic and cathodic reactions and electrode resistance losses. A typical anode used in the hydrodimerization process is 100mA/cn2
Approximately 2.2 µm is required at a current density of . In contrast, the hydrodimerization process of the present invention employs an anode that requires a voltage of approximately 1.8V, and a savings of approximately 0.4V is achieved.

Significant energy savings in the electrohydro-dimerization process are achieved as a result of these voltage reductions.The anode of the present invention uses NiC as the catalyst.

204, this particular catalyst can be synthesized from readily available metal salts. Additionally, this catalyst does not contain precious metals, unlike other commercial electrode systems, providing cost advantages. Thus, the adoption of energy saving electrodes according to the present invention represents an advance in electrochemical engineering for adiponitrile production.

Although the present invention has been described above with reference to certain preferred embodiments, the present invention is not limited to these embodiments (although various embodiments are possible within the scope of the present invention). This will be clear to those skilled in the art.

[Brief explanation of the drawing]

The drawing is a graph showing a comparison of the voltage between an anode including a NiCo2O4 catalyst according to the present invention and a known typical anode. 1...Curve according to known documents, 2...Curve according to the present invention Patent Applicant: International Fertil Cells Corporation

Claims (1)

[Scope of Claim] A method for hydrodimerizing acrylonitrile to produce adiponitrile in an electrochemical system in an electrolytic cell comprising an aqueous electrolyte, an anode, and a cathode, comprising: a) a cathode and an anode; b) maintaining a source of acrylonitrile at the cathode; c) maintaining a source of hydroxide ions at the anode; and d) passing a direct current through said system and causing a source of acrylonitrile at the cathode. the hydrodimerization of acrylonitrile to adiponitrile and the oxidation of hydroxyl ions at an anode, the anode containing polytetrafluoroethylene adhered to an electrically conductive substrate; A process for the hydrodimerization of acrylonitrile utilizing a layer of NiCo_2O_4, characterized in that the required anode voltage is less than about 2000 mV at a current density of 100 mA per cm^2 of anode area.